Is getting fit easier for some people?

While physical activity is an essential part of getting fit, it's not the whole story. An individual's fitness level also depends on how they respond to that activity, which is largely determined by their genes.

The landmark research in this field is the Heritage family study, begun in the 1990s. US and Canadian researchers recruited 481 sedentary people from 98 families, and subjected them to a rigorous 20-week training programme. They then put them through a battery of tests.

While many people's aerobic fitness improved dramatically, others showed a less marked response. The disheartening news is that about 1 in 10 showed no change whatsoever in their aerobic fitness, despite doing 45 minutes of vigorous exercise three times a week for the final six weeks of the programme (Journal of Applied Physiology, vol 87, p 1003).

The degree of response turned out to be largely down to the participants' genes. ...

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